ext4: avoid divide by zero when trying to mount a corrupted file system (503358ae) · Commits · 戴 / test

If s_log_groups_per_flex is greater than 31, then groups_per_flex will will overflow and cause a divide by zero error. This can cause kernel BUG if such a file system is mounted. Thanks to Nageswara R Sastry for analyzing the failure and providing an initial patch. http://bugzilla.kernel.org/show_bug.cgi?id=14287 Signed-off-by:

"Theodore Ts'o" <tytso@mit.edu> Cc: stable@kernel.org

fs/ext4/super.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -1673,14 +1673,14 @@ static int ext4_fill_flex_info(struct super_block *sb)
		size_t size;
		int i;

		if (!sbi->s_es->s_log_groups_per_flex) {
		sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex;
		groups_per_flex = 1 << sbi->s_log_groups_per_flex;

		if (groups_per_flex < 2) {
		sbi->s_log_groups_per_flex = 0;
		return 1;
		}

		sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex;
		groups_per_flex = 1 << sbi->s_log_groups_per_flex;

		/* We allocate both existing and potentially added groups */
		flex_group_count = ((sbi->s_groups_count + groups_per_flex - 1) +
		((le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks) + 1) <<

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